Cyclosporine is an immunosuppressive agent used to prevent rejection of transplanted organs. It has been used extensively in transplantation in the United States since it's release in December 1983. Following oral administration, the absorption of cyclosporine is highly variable. Neoral, a microemulsion formulation of cyclosporine, released in July 1995, demonstrates considerably reduced variability in cyclosporine pharmacokinetic parameters. Abbott cyclosporine is bioequivalent to the Neoral formulation, with a similar pharmacokinetic profile in healthy volunteers. This industry-sponsored study evaluated the pharmacokinetic profile and safety of Abbott cyclosporine in renal transplant recipients. Medically stable kidney transplant recipients at least six months post-transplantation were studied in an open-label conversion study that consisted of a screening period followed by (1) two weeks of dosing with twice-daily Neoral, (2) two weeks of dosing with twice-daily Abbott cyclosporine, and (3) one week of twice-daily Neoral. Twelve-hour pharmacokinetic profiles were performed on days 1, 14, 15, 28, 29. After completion of the study the study subjects continued on Neoral, as Abbott cyclosporine is an investigational drug. Cyclosporine trough blood levels were also obtained at screening and on days 7, 21, 35. Fifty subjects at 5 U.S. kidney transplant centers were to be enrolled.